Loss Of Winter Ice Linked To Colder Temperatures, Heavier Snows

Stick with me here...

We're getting to know all about the Polar Vortex - - Milwaukee was stuck at -13 degrees this morning, with a chill factor of -41 - - but a similar phenomenon happened last year and a leading scientist says it's appearing more often.

The event began exactly one year ago:

This phenomenon, known as a “sudden stratospheric warming event,” started on Jan. 6, but is something that is just beginning to have an effect on weather patterns across North America and Europe... 

Sudden stratospheric warming events take place in about half of all Northern Hemisphere winters, and they have been occurring with increasing frequency during the past decade, possibly related to the loss of Arctic sea ice due to global warming. Arctic sea ice declined to its smallest extent on record in September 2012.

I know, I know - - it all sounds contradictory and your conservative, climate-change denying friends radio talk show squawkers will mock it with closed minds from sealed studios, but here is the argument made by a leading scientist, and it's well worth considering:

“For reasons I don’t think we fully understand, the changes in the circulation that happen in the stratosphere [can] descend down all the way to the Earth’s surface,” said Judah Cohen, director of seasonal forecasting at Atmospheric and Environmental Research (AER) in Massachusetts.

As the polar stratosphere warms, high pressure builds over the Arctic, causing the polar jet stream to weaken. At the same time, the midlatitude jet stream strengthens, while also becoming wavier, with deeper troughs and ridges corresponding to more intense storms and high pressure areas. In fact, sudden stratospheric warming events even make so-called “blocked” weather patterns more likely to occur, which tilts the odds in favor of the development of winter storms in the U.S. and Europe.

Cohen was the lead author of a 2009 study that found that sudden stratospheric warming events are becoming more frequent, a trend that may be related to an increase in fall snow cover across Eurasia. The increase in snow cover has in turn been tied to the rapid loss of Arctic sea ice, since the increase in open water in the fall means that there is more atmospheric moisture available to fall as rain or snow.

Other experts put it this way:

As temperatures rise faster in the Arctic than at lower latitudes, this changes large-scale temperature and pressure gradients - which has consequences for northern hemisphere winter weather.

Professor Charles Greene from Cornell University tells us:

"Global warming has increased the loss of summer sea ice in the Arctic, which has altered atmospheric conditions in a manner that stacks the deck in favor of more severe winter outbreaks".

The pressure change alters atmospheric circulations, including the jet stream - a stream of fast-flowing air in the atmosphere. It also makes the jet stream's path meander more, which allows cold Arctic air to reach further south, affecting the climate in the mid-latitudes.

Scientists are just beginning to understand the effect quicker Arctic sea ice melt could have on northern hemisphere climate. While it's difficult to attribute any particular event to effects of the changing Arctic, [Rutgers University] professor [Jennifer] Francis tells us:

"If the summer ice covers disappears sooner than climate models project, I would expect to see Arctic amplification intensify sooner, and the effects on the large-scale circulation would become more conspicuous."

These phenomena also reminded me of a 2012 study which found that the decline in Great Lakes winter ice - - as temperatures warm - - has led to greater water evaporation and thus to an increase in lake effect snow.

So maybe it's not so hard to understand after all. But understanding it is a good thing.